1. Field of the Invention
The present invention relates to a plasma display panel used for displaying an image in a television receiver or a computer and a method for manufacturing the same.
2. Description of the Prior Art
FIG. 7 shows a conventional AC type plasma display panel. As is shown in FIG. 7, the conventional AC type plasma display panel (hereinafter, referred to as a panel) 1 is provided with a front substrate 3 and a back substrate 4 opposing each other separated by a discharge space 2. The front substrate 3 is a transparent glass substrate, on which a group of electrodes including pairs of belt-like scanning electrodes 7 and sustaining electrodes 8 covered with a dielectric layer 5 and a protective coating 6 are arranged in parallel. Belt-like data electrodes 9 are arranged in parallel on the back substrate 4 in the direction perpendicular to the scanning electrode 7 and the sustaining electrode 8. Belt-like spacers 10 are provided between the data electrodes 9 in order to separate data electrodes 9 and form the discharge space 2. Also, phosphors 11 are formed on the data electrodes 9 towards the side of the spacers 10. Mixed gas of xenon and at least one of the rare gases selecting from helium, neon and argon is sealed in the discharge space 2.
In this panel 1, an image display is seen from the front substrate 3 side. Ultraviolet light, which is generated by discharges between the scanning electrode 7 and the sustaining electrode 8 in the discharge space 2, excites the phosphors 11, then visible light from this phosphors 11 is used for the light emitted by the display.
In general, a contrast ratio of the display in a bright ambience needs to be at least 50:1. When the inventors measured the brightness at the illumination of 150 lxc3x97 of an AC type plasma display panel using a conventional transparent glass substrate (mean transmittance for visible light is approximately 94%) as the front substrate, the maximum brightness of the light emitted by the display was 450 cd/m2 and the background brightness due to reflection of external lights was 16 cd/m2. Accordingly, the contrast ratio was as small as about 28:1. In this case, the mean transmittance for visible light means a mean value of the transmittance within the wavelength range of the visible light (360 to 830 nm), and, in the following, the mean transmittance refers to the mean transmittance for visible light.
As a method for making the contrast ratio at least 50:1, a glass substrate with a dark color can be used as the front substrate. For example, the mean transmittance r of this dark color glass substrate can be calculated with the formula below so that the contrast ratio may be 50:1.
450(r/0.94)/{16(r2/0.94)}=50
r=0.52 is obtained with this formula. Therefore, the required mean transmittance of the front substrate is approximately 50%.
However, as is described above, the scanning electrodes 7, the sustaining electrodes 8, the dielectric layer 5 and the protective coating 6 are formed on the front substrate 3. During their forming step, a pattern defect in the scanning electrodes 7 and the sustaining electrodes 8, an internal defect and dust in the dielectric layer 5 or the protective coating 6 are checked for. A defect checking device for this purpose has been automated with image recognition technologies. In order to increase the defect detection rate, an appropriate illumination from both surfaces of the front substrate 3 is necessary. When a glass substrate with a mean transmittance of 50% is used as the front substrate 3, especially the illumination from the front side of the front substrate 3 (the side of the front substrate 3 that opposes the one on which the scanning electrodes etc. are formed) is not appropriate, resulting in a considerable decrease in the defect detection rate with this defect checking device.
In addition, as another method for making the contrast ratio at least 50:1, a filter made of a dark color glass with a mean transmittance of approximately 50% can be provided on the front surface of the transparent front substrate 3. However, when an image with black and white displays adjacent each other is displayed on this panel, the white display is blurred in the region near the border that should be the black display. This is called halation.
It is an object of the present invention to solve the problems above and to provide a plasma display panel and a method for manufacturing the same, which realizes a preferable display with less halation and high contrast and improves the detection rate of a defect and dust in the scanning electrodes and the sustaining electrodes, which are formed on the front substrate.
The plasma display panel in accordance with the present invention includes a front substrate, a back substrate opposing the front substrate and separated therefrom by a discharge space, and a front filter provided on a front side of the front substrate. Mean transmittances for visible light of the front substrate and the front filter are 60 to 80% respectively.
With this configuration, halation and external light source reflection lessen, contrast increases, and reflected images can be suppressed. Also, a defect and a dust in the scanning electrodes and the sustaining electrodes, which are formed on the front substrate, can be detected with a high probability.
The method for manufacturing the plasma display panel in accordance with the present invention includes forming scanning electrodes and sustaining electrodes on a front substrate with a mean transmittance for visible light of 60 to 80%, checking for defects by illuminating from a front side of the front substrate, forming a dielectric layer and a protective coating covering the scanning electrodes and the sustaining electrodes, placing a back substrate in opposition to the front substrate and sealing a place therebetween, sealing a gas between the front substrate and the back substrate, and providing a front filter with a mean transmittance for visible light of 60 to 80% in the front side of the front substrate.
With this method, a defect and dust in the scanning electrodes and the sustaining electrodes, which are formed on the front substrate, can be detected with a high probability, leading to a reliable inspection in the manufacturing step.